1. Field of the Invention
This invention relates to a method of simultaneously making multiple microelectronic ceramic substrates by stacking the substrates prior to firing with an intervening thermally degradable interface layer, and to a method of making the interface layer. The invention also relates to the microelectronic ceramic substrates and to the interface layers made by the methods of the invention.
2. Description of Related Art
In the ceramic electronic industry, multilayer ceramic (MLC) technology is typically used to create three-dimensional circuitry in ceramic substrates for microelectronic devices such as integrated circuits and ceramic capacitors. The three-dimensional circuitry in the ceramic substrate is made by applying a conductive material in a circuit pattern on a ceramic/polymer composite sheet. The ceramic/polymer composite sheet is known as a "green sheet" and may have a number of via holes punched in it to allow vertical connection between the conductive material on adjacent sheets. The green sheets are stacked in a designated order and laminated together under appropriate heat and pressure to form a laminate which can be handled as a unified structure.
To produce the final ceramic material, the laminated ceramic/polymer composite is fired. The firing includes heating to remove the polymer, followed by heating to a higher temperature to sinter and densify the ceramic.
The laminate may make up a single large electronic component, but more often, it is a repetition of multiple components located adjacent to one another which need to be cut apart into individual substrates for subsequent use. This cutting may be done in the unfired stated, in the fired state or at some point therebetween.
Cutting laminates in the unfired state is the easiest, based on a criteria of laminate hardness, However, debris is generated during the cutting which will remain on the fired units. This debris is detrimental to electrical conductivity and may result in defective substrates.
Cutting laminates in the fired state can eliminate the debris problem, but the ceramic is now very hard and cutting efficiency is greatly reduced. An alternative method is to partially cut the laminate when unfired. This produces less debris. After firing, the laminate can be broken in a controlled manner along the partial cuts. However, this method also has disadvantages because of the debris generated prior to firing and the fracturing and cracking that occurs during the breaking process.
It would be desirable to provide some method of protecting the surface of the substrates against debris contamination so that cutting could be done in the unfired state. It would also be desirable to provide some means of allowing the individual substrates to be completely cut apart prior to firing, to avoid the disadvantages of fracturing when breaking them apart, while still holding the substrates together as a unitary structure prior to firing for convenient handling of the laminate.
The number of individual units produced by the methods described above is limited by the physical size of the laminate that can be produced. For a fixed maximum laminate size, more individual units can be produced if they are smaller. Given a fixed laminate size and fixed cycle times for the ceramic sintering process the output of relatively large individual units is low.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of increasing the number of units which can be produced during each firing cycle.
It is another object of the present invention to reduce the problems resulting from debris contamination.
A further object of the present invention is to eliminate or reduce the problems with fractured surfaces when partially cut laminates are broken apart after firing.
Still other objects and advantages of the invention will be in part obvious and in part apparent from the specification.